This invention relates to water-based coating compositions for exterior surfaces which upon application quickly develop resistance to being washed out by precipitation. These compositions comprise an aqueous dispersion of water-insoluble latex polymer and a flocculating solution. When compared to solvent-based coatings, water-based coatings have the advantage of lower emissions of toxic solvents and easy cleanup of site and equipment. However, water-based coatings are vulnerable to water damage during and immediately after application.
Immediately after application, roof mastics are particularly vulnerable to being washed out by unanticipated precipitation. A substantial need exists for water-based roof mastics and other exterior water-based coatings products which resist washout immediately after application or shortly thereafter. This property is referred to as early washout resistance.
In U.S. Pat. No. 4,571,415, a water-soluble salt of a multivalent complex ion having labile, volatile ligands such as zinc ammonium complex ion is added to the roof mastic composition. It is believed that early washout resistance results from multivalent metal ion precipitation of the anionic polymers used to disperse pigments and that the multivalent metal ions become available for such precipitation as the complex metal ion is shifted through the various equilibria linking it to metal ion. The ligand, for example, is believed to be lost at the surface of the applied coating or caulk to the atmosphere.
There are some problems with incorporating the flocculant into the roof mastic composition before it is applied to the roof, as in U.S. Pat. No. 4,571,415. Zinc tetramine bicarbonate requires high formulation pH (e.g., 10) in order to maintain shelf stability. There also have been objections to ammonia odor. Use of a strongly cationic flocculant is precluded because colloidal stability must be maintained until the mastic is applied. This necessitates a latent flocculant, whose action must of necessity be delayed to some degree.
In U.S. Pat. No. 4,386,992, a cosprayed gelling agent is used to increase initial bond strength of an adhesive, such as when a polyurethane foam is bonded onto a steel board of an automobile ceiling.
In U.S. Pat. No. 3,823,024, a temporary protective coating that is easily stripped is disclosed. This coating is produced by spraying a stream of latex and a stream of coagulant onto the surface along with a debonding agent.